Generally, liquefied natural gas presents a viable fuel alternative to, for example, gasoline and diesel fuel. More specifically, LNG may be utilized as an alternative fuel to power certain vehicles and/or power generation plants. Accordingly, there has been an increasing demand for LNG dispensing stations. To meet this demand, a greater number of LNG dispensing stations are being built in increasingly remote locations in order to service the industries that depend on LNG fuel. This presents a range of issues, including station maintenance, safety, and accuracy.
Storing LNG in dispensing stations and vehicle tanks requires specialized equipment because LNG is stored at temperatures of below approximately −200° F. (−130° C.). Further, LNG dispensers should be able to do this with minimized venting of LNG to the atmosphere, because venting wastes LNG and poses potential environmental and safety concerns.
While storing bulk quantities of LNG at low pressures is more convenient, many engines cannot operate efficiently under low pressures. Accordingly, LNG may be stored in vehicle tanks in an elevated saturated state in order to maintain the desired pressure while the vehicle is in motion. An elevated LNG saturation state generally occurs by heating the LNG prior to dispensing.
LNG is typically transferred from a bulk storage tank, saturated, and dispensed to a vehicle tank through pumps or other mechanical or rotating equipment (herein generally referred to as pumps) to achieve the pressure gradients required for transfer, as well as to assist with LNG saturation prior to dispensing. Such equipment, however, may be expensive to purchase and maintain, adding to maintenance and operation costs of dispensing stations. Pumps require significant energy to run, as well as proper cooling and lubrication. Accordingly, such devices add to the size, weight, and complexity of dispensing systems.
Accurately measuring the amount of LNG dispensed for use also poses a primary concern in commercializing LNG. Particularly, the National Institute of Standards and Technology of the United States Department of Commerce has developed guidelines for federal Weights and Measures certification, whereby dispensed LNG must be metered on a mass flow basis with a certain degree of accuracy.
Accordingly, prior art devices require improvement to achieve compact and easy-to-maintain dispensing systems capable of accurately dispensing pressurized fluids without the use of pumps. The dispensing systems described herein aim to overcome these and other limitations in the prior art in an economical and safe fashion.